This invention concerns an apparatus for detecting the fact that a moving ball or other game piece has crossed a boundary or play determinative line on a playing field. It is particularly applicable to the game of football wherein it is important to the play of the game if a ball has advanced 10 yards or has crossed the goal line.
It is an object of the invention to provide an apparatus which will accurately and reliably detect the fact that a playing object has reached or crossed a linear boundary of a playing field. In particular it is an object of the invention to provide an apparatus which is not dependent on visual or optical observation and will function without interference by intervening players on the field.